1. Field of the Invention
The present invention relates to an image processing system, and more particularly, to a system and method for converting a gray-level image into a binary image.
2. Description of the Prior Art
Many image-processing devices need to convert gray-level images into binary images. Line-art/bi-level conversion method and half-tone conversion method are the most commonly used two conversion methods. The line-art/bi-level method uses a gray-level threshold value between 0 and 255 to convert a gray-level pixel. A gray-level pixel with a value greater than the threshold is converted into 1, otherwise it is converted into 0. The converted binary image usually shows a character of strong contrast. Such a conversion method is ideal for text image conversion since the edges of text data usually show strong contrast character, but it is inappropriate for converting graphic images because graphic images usually have a lot of continuous gray-level variations.
The half-tone conversion method includes dither method, error diffusion method, and correlative density assignment of adjacent pixels (CAPIX). The half-tone conversion method can effectively reflect continuous variations of gray levels and can thus be adequately used to convert graphic images. However, in converting text images it will blur the edges of text data and thus should be avoided.
Text and graphic images need to use different conversion methods for converting each of them into a binary image. But since the prior art image conversion method can only be used to convert a complete image each time, a user must make a decision to select a single conversion method which is suitable for converting one type of images even though the image to be converted may contain both types of images.